Preparation method of flame-retardant waterproof urea-formaldehyde resin adhesive

Abstract

The invention discloses a preparation method of a flame-retardant waterproof urea-formaldehyde resin adhesive, which is prepared from the following raw materials in parts by weight: 100 to 120 parts of urea, 180 to 220 parts of formaldehyde-37% aqueous solution, 10 to 15 parts of melamine, 8 to 12 parts of ammonium dihydrogen phosphate, 3 to 5 parts of polyvinyl alcohol, a proper amount of sodium hydroxide, a proper amount of ammonium chloride and 150 to 200 parts of water. The invention further discloses a preparation method of the flame-retardant waterproof urea-formaldehyde resin adhesive. The preparation method comprises the following steps: S1, prepolymerization reaction; s2, polycondensation reaction; s3, flame-retardant and waterproof modification; and S4, carrying out post-treatment. The urea-formaldehyde resin adhesive can form an expansive carbon layer in the combustion process, oxygen and heat transfer are effectively isolated, the flame retardant property of the adhesive is remarkably improved, the oxygen index of the prepared adhesive reaches 30% or above, and the prepared adhesive meets the standard of flame-retardant materials.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesive preparation, and particularly relates to a preparation method of a flame-retardant and waterproof urea-formaldehyde resin adhesive. Background Art

[0002] Urea-formaldehyde resin adhesives are the most widely used adhesives in the manufacture of wood-based panel products such as particle boards and fiber boards, accounting for more than 90% of the consumption of wood-based panel adhesives.

[0003] For current traditional urea-formaldehyde resin adhesives, they have problems of poor flame retardancy and water resistance. In some places with high requirements for fire safety and moisture protection, such as interior building decoration and shipbuilding, their applications are restricted. Although there are currently some methods to modify urea-formaldehyde resin to improve its flame retardancy and water resistance, there are generally problems such as complex processes, high costs, or unsatisfactory effects. Accordingly, the present invention proposes a preparation method of a flame-retardant and waterproof urea-formaldehyde resin adhesive. Summary of the Invention

[0004] The purpose of the present invention is to solve the deficiencies existing in the prior art, and to propose a preparation method of a flame-retardant and waterproof urea-formaldehyde resin adhesive.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A flame-retardant and waterproof urea-formaldehyde resin adhesive is prepared from the following raw materials in parts by weight: 100 - 120 parts of urea, 180 - 220 parts of 37% aqueous formaldehyde solution, 10 - 15 parts of melamine, 8 - 12 parts of ammonium dihydrogen phosphate, 3 - 5 parts of polyvinyl alcohol, an appropriate amount of sodium hydroxide, an appropriate amount of ammonium chloride, and 150 - 200 parts of water. Among them, the urea is granular urea with an industrial purity of not less than 99%, and its particle size range is 0.5 - 1.5 mm, ensuring rapid and uniform dissolution in the reaction system. The impurity content of the formaldehyde aqueous solution is less than 0.5%, and the methanol content in the formaldehyde aqueous solution is controlled at 0.1% - 0.3% to optimize the reaction process.

[0007] Preferably, the molar ratio of urea to formaldehyde is 1:1.5 - 1.8, and during the reaction process, formaldehyde is added in batches. The first addition amount is 80% - 90% of the total amount, and the remaining part is slowly added dropwise during the polycondensation reaction stage according to visual phenomena such as the foam state and color change in the reaction system, combined with the viscosity change, to accurately control the reaction rate and product structure.

[0008] The above preparation method of a flame-retardant and waterproof urea-formaldehyde resin adhesive includes the following steps:

[0009] S1. Prepolymerization reaction: In a reaction kettle equipped with a stirrer, a thermometer, and a reflux condenser, formaldehyde solution and water are added. After stirring evenly, the pH value is adjusted to 7.5 - 8.5 with sodium hydroxide solution, and then 60% - 70% of the total amount of urea is added. The temperature is raised to 80 - 85°C, and the reaction is maintained for 30 - 40 minutes. During this process, the stirring speed is controlled at 150 - 200 revolutions per minute, and the pressure inside the reaction kettle is maintained at 0.05 - 0.1 MPa to promote the efficient progress of the reaction;

[0010] S2. Polycondensation reaction: The pH value of the reaction system is adjusted to 4.8 - 5.2 with ammonium chloride solution, and the temperature is raised to 90 - 95°C for polycondensation reaction. When the viscosity reaches 0.1 - 0.15 Pa·s, the remaining urea is added, and the reaction continues for 15 - 20 minutes. During the reaction process, in addition to continuously monitoring the change of the conductivity of the system, the change of the light transmittance of the reaction system is also monitored online to assist in judging the reaction progress and ensure that the reaction reaches the expected degree;

[0011] S3. Flame-retardant and waterproof modification: Melamine and ammonium dihydrogen phosphate are added to the reaction kettle and stirred evenly. The reaction is carried out at 90 - 95°C for 30 - 40 minutes. During this period, ultrasonic assistance is used for dispersion, with a frequency of 20 - 40 kHz, and at the same time, the power density of the ultrasonic wave is controlled at 0.5 - 1.5 W / cm 2 , so that the flame-retardant and waterproof additives can be more evenly dispersed in the system and enhance the modification effect;

[0012] S4. Post-treatment: After the reaction is completed, the temperature is lowered to 50 - 60°C, and the pH value is adjusted to 7.0 - 7.5 with sodium hydroxide solution. Then polyvinyl alcohol is added, stirred and dissolved, and then stirred for 30 - 40 minutes to obtain the finished product of flame-retardant and waterproof urea-formaldehyde resin adhesive. The post-treatment stage is carried out under a nitrogen protection atmosphere, and the flow rate of nitrogen is controlled at 10 - 20 L / min to prevent the adhesive from being oxidized or interfered by other impurities during the post-treatment process.

[0013] Preferably, in the prepolymerization reaction stage, the reaction degree is controlled by measuring the viscosity of the reaction system with a professional rotational viscometer. The selected rotational viscometer has an accuracy of up to ±0.001 Pa·s, the rotor model is No. 2, and the rotational speed is 60 revolutions per minute. Before measuring the viscosity, the viscometer needs to be calibrated to ensure the accuracy of the measurement data.

[0014] Preferably, in the prepolymerization reaction stage, the reaction degree is controlled by measuring the viscosity of the reaction system with a professional rotational viscometer. The selected rotational viscometer has an accuracy of up to ±0.001 Pa·s, the rotor model is No. 2, and the rotational speed is 60 revolutions per minute. Before measuring the viscosity, the viscometer needs to be calibrated to ensure the accuracy of the measurement data.

[0015] Preferably, in the flame-retardant and waterproof modification stage, Fourier transform infrared spectroscopy is used to monitor the reaction degree. The change of characteristic peaks is observed to judge the progress of the reaction. FT-IR spectral data is collected every 10 minutes. When analyzing the spectral data, not only the intensity of the characteristic peaks representing the cross-linked structure of melamine and urea-formaldehyde resin is concerned, but also the changes in peak shape and peak position are combined to comprehensively determine whether the reaction is basically completed.

[0016] Preferably, in the prepolymerization reaction and polycondensation reaction stages, an on-line infrared spectrometer is used to monitor the changes of functional groups in the reaction system in real time. By analyzing the intensity and displacement of the characteristic peaks of specific functional groups, the progress and degree of the reaction are accurately judged to more precisely control the reaction time and conditions, ensuring the consistency and stability of the product.

[0017] Preferably, in the post-treatment stage, the obtained finished flame-retardant and waterproof urea-formaldehyde resin adhesive is filtered using a microporous filter with a pore size of 0.1 - 0.5 microns to remove possible impurities, unreacted particles, and aggregates in the adhesive, improving the purity and uniformity of the adhesive, and further enhancing the quality and performance of the adhesive, ensuring better bonding effect and stability in practical applications.

[0018] Preferably, the adhesive layer formed after the curing of the adhesive has good flexibility. Through the flexibility test, its flexibility index reaches 1 - 2 mm, which can effectively resist the internal stress generated by the deformation of the substrate, prevent the adhesive layer from cracking, and improve the durability of the bonding structure.

[0019] The present invention has the following beneficial effects:

[0020] 1. By adding melamine and ammonium dihydrogen phosphate, an expanded carbon layer is formed during the combustion process, effectively isolating the transfer of oxygen and heat, and significantly improving the flame retardancy of the adhesive. After testing, according to the GB / T2406.2 - 2009 standard, the oxygen index of the prepared adhesive reaches more than 30%, meeting the standard of flame-retardant materials. In the examples, the oxygen index of the adhesive reaches 31 - 33%, belonging to flame-retardant materials. For example, in the initial stage of a building fire, it can effectively delay the spread of the fire, gain more time for personnel evacuation, reduce the life and property losses caused by the fire, and greatly enhance the fire safety guarantee.

[0021] 2. The addition of polyvinyl alcohol forms a stable network structure and reduces the water absorption rate of the adhesive. According to the GB / T17657-2013 standard test, after being immersed in water for 24 hours, its water absorption rate is less than 8%, and the water absorption rate of the adhesive in the embodiment is as low as 6.5-7.5%, with excellent waterproof performance. For example, the adhesive in the embodiment is used to bond the plates in the cabin of a ship, which can effectively resist the penetration of seawater, prevent the corrosion of metal parts, extend the overall service life of the ship, reduce the frequency and cost of maintenance, and avoid the problems of debonding and deformation due to moisture after furniture is used, so as to maintain the beauty and use function.

[0022] 3. Adhesives prepared by common methods are difficult to use in special scenarios with strict requirements on flame retardancy, waterproofness and bonding strength due to performance limitations. The adhesives of the embodiments can be used in fire partition walls of buildings, fire bulkheads of ships, waterproof reinforcement of outdoor furniture and other scenarios due to their excellent comprehensive performance. For example, in outdoor wooden landscape facilities, which need to withstand sun, rain and large external forces, the adhesives of the embodiments can ensure long-term stable bonding and have flame retardancy to prevent fires caused by discarded cigarette butts, thereby expanding the application possibilities of adhesives in different fields and meeting diverse needs.

[0023] 4. During the preparation process, precise monitoring methods such as rotational viscometer and Fourier transform infrared spectrometer, as well as strict control of multiple parameters such as reaction temperature, pH value, time, etc., are used to ensure that the quality of each batch of products is highly consistent. From the performance test results, under different test environment temperatures of 15℃-35℃ and humidity of 30%-70%RH, the oxygen index fluctuates very little, the waterproof performance is slightly affected by water temperature, and the wood shear strength is stable within the common moisture content range. This allows the adhesive to maintain stable and reliable performance in different regions, seasons and under different usage conditions, greatly reducing the quality risks and usage problems caused by product performance fluctuations, and providing solid guarantees for various applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a step diagram of a method for preparing a flame retardant and waterproof urea-formaldehyde resin adhesive proposed by the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0026] Embodiment 1:

[0027] 1. Recipe:

[0028] Urea: Industrial-grade high-purity urea is selected, with a purity reaching over 99.5%. Its particles are uniform, with a particle size between 0.8 - 1.2 mm. Urea of this specification can dissolve quickly in the reaction system to ensure the efficient progress of the reaction. The dosage of 100 parts is accurately determined according to the molar ratio with formaldehyde and the overall reaction requirements. In the entire adhesive system, urea serves as the main reactant and participates in forming the basic structure of urea-formaldehyde resin.

[0029] Formaldehyde (37% aqueous solution): An aqueous formaldehyde solution with stable quality is used. Its impurity content is less than 0.3%, and the formaldehyde content is precisely controlled at around 37%. The dosage of 180 parts forms a molar ratio of 1:1.5 - 1.8 with urea, and this ratio has a crucial impact on the degree of polymerization and properties of urea-formaldehyde resin. Formaldehyde undergoes a polycondensation reaction with urea in the reaction to construct the main framework of the adhesive.

[0030] Melamine: As a key component for flame-retardant modification, fine powder with a particle size between 20 - 40 microns and a purity as high as 99% is selected. The addition amount of 10 parts can crosslink with urea-formaldehyde resin in the subsequent reaction to form a stable flame-retardant structure. During the combustion process, melamine decomposes to produce nitrogen-containing gases, diluting the oxygen concentration, and at the same time promoting the formation of a carbon layer, effectively enhancing the flame-retardant performance of the adhesive.

[0031] Ammonium dihydrogen phosphate: It is a white crystalline powder with a purity of over 98%. 8 parts of ammonium dihydrogen phosphate decompose at high temperatures to produce phosphoric acid, ammonia, and water, etc. Phosphoric acid can catalyze the dehydration and carbonization of substrates such as wood to form a carbonaceous heat-insulating layer, and ammonia plays a role in diluting oxygen, synergistically enhancing the flame-retardant effect with melamine.

[0032] Polyvinyl alcohol (PVA - 1788): Polyvinyl alcohol with a degree of polymerization of about 1700 and a degree of alcoholysis of 88% is selected. The hydroxyl groups on its molecular chain can form hydrogen bonds with the molecules of urea-formaldehyde resin. The dosage of 3 parts forms a network structure in the system, effectively improving the waterproof performance of the adhesive and enhancing the adhesion between the adhesive and the substrate.

[0033] Sodium hydroxide: Analytical pure grade sodium hydroxide is used to adjust the pH value of the reaction system. In the early stage of the reaction, the pH value is adjusted to 7.5 to provide a suitable alkaline environment for the prepolymerization reaction of urea and formaldehyde and promote the formation of hydroxymethylurea.

[0034] Water: Deionized water is used. 150 parts of water serve as the reaction medium, which can not only dissolve various raw materials but also play a role in heat transfer and dispersion during the reaction to ensure the uniform progress of the reaction.

[0035] 2. Preparation steps:

[0036] S1. Prepolymerization reaction: In a reaction kettle equipped with a high-precision stirrer, a thermometer, and an efficient reflux condenser, formaldehyde solution and deionized water are added. Stirring is started, and the stirring speed is set at 180 revolutions per minute to fully mix the solution evenly. The pH value is slowly adjusted to 7.5 with sodium hydroxide solution, and a precision pH meter is used to monitor it in real time during the process. Subsequently, 60% of urea is added, and the temperature increase program is started. The temperature is increased to 80 °C at a rate of 2 °C per minute and kept at this temperature for a reaction for 30 minutes. During the reaction process, the viscosity of the reaction system is measured by a rotational viscometer. When measuring, a No. 2 rotor is selected, and the rotational speed is 60 revolutions per minute. When the viscosity reaches 0.06 Pa·s, the prepolymerization reaction reaches the expected degree.

[0037] S2. Polycondensation reaction: The pH value of the reaction system is adjusted to 4.8 with ammonium chloride solution, and continuous stirring is carried out during the adjustment process. Then the temperature is increased to 90 °C at a rate of 3 °C per minute for the polycondensation reaction. During the reaction process, the viscosity of the system is continuously monitored. When the viscosity reaches 0.12 Pa·s, the remaining 40% of urea is added, and the reaction continues for 15 minutes. In this stage, the molecular weight and cross-linking structure of the urea-formaldehyde resin are precisely controlled by controlling the reaction temperature, pH value, and time.

[0038] S3. Flame-retardant and waterproof modification: Melamine and ammonium dihydrogen phosphate are added to the reaction kettle. The ultrasonic dispersion device is started, the frequency is set at 30 kHz, and the power is 100 W. Stir evenly and react at 90 °C for 30 minutes. During the reaction process, the reaction degree is monitored in real time by a Fourier transform infrared spectroscopy (FT-IR) instrument. Spectral data is collected every 5 minutes. By observing the change in the intensity of the characteristic peak representing the cross-linking structure of melamine and urea-formaldehyde resin, it is judged whether the reaction reaches the expected effect.

[0039] S4. Post-treatment: After the reaction is completed, the temperature decrease program is started, and the temperature is decreased to 50 °C at a rate of 5 °C per minute. The pH value is adjusted to 7.0 with sodium hydroxide solution, and then polyvinyl alcohol is added. The stirring speed is adjusted to 150 revolutions per minute. After stirring and dissolving, continue stirring for 30 minutes to fully disperse the polyvinyl alcohol and interact with other components in the system, and finally obtain the finished product.

[0040] 3. Performance testing:

[0041] Oxygen Index Test: According to the GB / T2406.2-2009 standard, the prepared adhesive was evenly applied on a standard wood sample with dimensions of 150 mm in length × 10 mm in width × 4 mm in thickness to make a test specimen. In an oxygen index measuring instrument, the mixing ratio of oxygen and nitrogen was precisely adjusted, the specimen was ignited, and the lowest oxygen concentration when the specimen could just maintain combustion was recorded. After multiple repeated tests and taking the average value, the oxygen index of the adhesive in this example was 31%. In an environment with a temperature of 15°C - 35°C, the oxygen index fluctuated within ±0.5%, showing good temperature stability.

[0042] Water Absorption Test: According to the GB / T17657-2013 standard, 5.00 g of the cured adhesive was taken, accurately weighed, and completely immersed in deionized water at 20°C for 24 hours. After taking it out, the surface moisture was gently blotted dry with filter paper and weighed again. Calculated by the formula "Water Absorption = (Mass after immersion - Mass before immersion) ÷ Mass before immersion × 100%", the water absorption of the adhesive in this example was 7.5%. In the range of environmental humidity of 30% - 70%RH, the change in water absorption was within ±0.3%, indicating that its waterproof performance was less affected by humidity.

[0043] Wood Bonding Shear Strength Test: According to the GB / T9846.4-2015 standard, two standard wood specimens with dimensions of 100 mm in length × 25 mm in width × 15 mm in thickness were selected. The adhesive was evenly coated on the wood bonding surface, and the coating thickness was controlled at 0.2 - 0.3 mm. A pressure of 0.5 MPa was applied and cured at room temperature for 24 hours. A universal material testing machine was used to measure the shear strength of the wood bonding parts, the loading rate was 1 mm / min, the failure load was recorded and the shear strength was calculated. After multiple tests, the shear strength of the adhesive to wood in this example was 1.25 MPa. When testing common wood species such as pine, birch, and oak, the shear strength fluctuated between 1.20 - 1.28 MPa, and it could better adapt to different wood materials.

[0044] Example Two:

[0045] 1. Formula:

[0046] Urea: 110 parts, with the same purity and particle size as in Example 1. In this example, according to the adjusted formaldehyde dosage and reaction requirements, the urea ratio was appropriately increased to optimize the structure and performance of the urea-formaldehyde resin.

[0047] Formaldehyde (37% aqueous solution): 200 parts. Further optimizing the molar ratio with urea affected the reaction process and product performance.

[0048] Melamine: 12 parts. Increasing the melamine dosage to further improve the flame retardancy performance.

[0049] Ammonium dihydrogen phosphate: 10 parts. With the increase in the dosage of melamine, adjust the dosage of ammonium dihydrogen phosphate to strengthen the flame retardant synergistic effect.

[0050] Polyvinyl alcohol (PVA-1788): 4 parts. Appropriately increase the dosage of polyvinyl alcohol to enhance the waterproof and adhesion properties.

[0051] Sodium hydroxide: appropriate amount, used to adjust the pH value to 8.0 to provide different alkaline environments for the prepolymerization reaction.

[0052] Ammonium chloride: appropriate amount, adjust the pH value to 5.0, which affects the rate and degree of the polycondensation reaction.

[0053] Water: 180 parts, adjust the dosage of the reaction medium according to the overall formula

[0054] 2. Preparation steps:

[0055] S1. Prepolymerization reaction: Add formaldehyde solution and water to the reaction kettle, stir evenly, and the stirring speed is 190 revolutions per minute. Use sodium hydroxide to adjust the pH value to 8.0, add 65% urea, and heat up to 83°C at a rate of 2.5°C per minute, and keep the temperature for 35 minutes. During this period, monitor the viscosity with a viscometer until it reaches 0.07 Pa·s.

[0056] S2. Polycondensation reaction: Use ammonium chloride to adjust the pH value to 5.0, heat up to 92°C, and when the viscosity reaches 0.13 Pa·s, add the remaining urea and continue the reaction for 18 minutes.

[0057] S3. Flame retardant and waterproof modification: Add melamine and ammonium dihydrogen phosphate, the ultrasonic dispersion frequency is 35 kHz, the power is 120 W, react at 92°C for 35 minutes, and monitor the reaction by FT-IR.

[0058] S4. Post-treatment: Cool down to 55°C, adjust the pH value to 7.2, add polyvinyl alcohol, and stir for 35 minutes to obtain the finished product.

[0059] 3. Performance testing:

[0060] Oxygen index test: Make specimens according to the standard for testing, and the oxygen index is 32%. In the temperature range of 10°C - 40°C, the oxygen index fluctuation does not exceed ±0.4%, and the stability is good.

[0061] Water absorption rate test: Test according to the standard, and the water absorption rate is 7.0%. In the humidity environment of 20% - 80% RH, the change in water absorption rate is controlled within ±0.2%, and the waterproof performance is stable.

[0062] Wood bonding shear strength test: According to the standard test, the shear strength is 1.3MPa. Tests on woods of different densities show that the shear strength on low-density wood is 1.28MPa, on medium-density wood is 1.31MPa, and on high-density wood is 1.33MPa, which can effectively adapt to all types of wood.

[0063] Embodiment three:

[0064] 1. Recipe:

[0065] Urea: 120 parts. Further increase the amount of urea to explore the effect on the performance of the adhesive.

[0066] Formaldehyde (37% aqueous solution): 220 parts, increase the amount of formaldehyde accordingly to maintain a suitable molar ratio.

[0067] Melamine: 15 parts, increase the amount of flame retardant.

[0068] Diammonium phosphate: 12 parts, synergistic with melamine to enhance the flame retardant effect.

[0069] Polyvinyl alcohol (PVA-1788): 5 parts, increasing the polyvinyl alcohol content to optimize waterproof performance.

[0070] Sodium hydroxide: appropriate amount, adjust pH to 8.5.

[0071] Ammonium chloride: appropriate amount, adjust pH to 5.2.

[0072] Water: 200 parts, to adjust the amount of reaction medium.

[0073] 2. Preparation steps:

[0074] S1. Prepolymerization: Mix formaldehyde solution and water in a reactor, stir at 200 rpm, adjust pH to 8.5, add 70% urea, heat to 85°C at a rate of 3°C / min, keep warm for 40 minutes, and the viscosity reaches 0.08 Pa·s.

[0075] S2. Condensation reaction: adjust the pH value to 5.2, raise the temperature to 95°C, and when the viscosity reaches 0.15 Pa·s, add the remaining urea and continue the reaction for 20 minutes.

[0076] S3, flame retardant and waterproof modification: add melamine and diammonium phosphate, ultrasonic dispersion frequency 40kHz, power 150W, react at 95℃ for 40 minutes, and monitor the reaction by FT-IR.

[0077] S4, post-treatment: cool to 60°C, adjust pH to 7.5, add polyvinyl alcohol, and stir for 40 minutes to obtain the finished product.

[0078] 3. Performance test:

[0079] Oxygen index test: The oxygen index obtained from the test is 33%. During the extreme temperature test from 5°C to 45°C, the oxygen index fluctuates only within ±0.3%, and the flame retardant performance is stable.

[0080] Water absorption test: According to the standard test, the water absorption is 6.5%. When the humidity changes from 10% to 90% RH, the change in water absorption is within ±0.15%, and the waterproof performance is excellent.

[0081] Wood bonding shear strength test: According to the standard test, the shear strength is 1.35 MPa. When tested on woods with different moisture contents (6% - 18%), the shear strength remains between 1.32 - 1.38 MPa, and it is less affected by the moisture content.

[0082] Based on the three examples, it can be seen that the flame retardant and waterproof urea - formaldehyde resin adhesive of the present invention shows significant beneficial effects in many aspects. In the fields of interior building decoration and shipbuilding, fire safety is of crucial importance. The oxygen index of the adhesive in the examples is as high as 31 - 33%, far exceeding that of ordinary adhesives, which is 20 - 25%. In the building fire simulation experiment, such as in the hotel guest room scenario, the wall decoration materials pasted with this adhesive only slightly carbonize within 5 minutes when the fire source approaches, and there is no open - flame combustion, thus winning precious time for personnel evacuation. In the high - fire - risk areas of ships, such as the engine room, the heat - insulating plates bonded with this adhesive can effectively prevent the flame from penetrating, delay the spread of fire, reduce the catastrophic consequences of the fire, and greatly improve the fire safety level.

[0083] Furthermore, whether it is a ship that is long - term eroded by seawater or furniture that faces daily humidity changes, the performance of ordinary adhesives rapidly deteriorates due to their high water absorption rate (15 - 20%). However, the water absorption rate of the adhesive in the examples is as low as 6.5 - 7.5%. In the actual application of bonding ship cabin plates, after two years of sea voyages, the plates are closely fitted, and there is only slight rust on the metal frame, effectively reducing the maintenance frequency and cost. In terms of furniture, taking a wooden wardrobe as an example, in the simulated environment of the southern plum rain season, the furniture using the adhesive in the examples has a firm bonding part after a three - month experimental period, the wood does not deform, and it maintains its beauty and usability, extending its service life.

[0084] Furthermore, adhesives prepared by ordinary methods are difficult to meet the stringent requirements for flame retardancy, waterproofing, and bonding strength in special scenarios. In the construction field, during the construction of fire compartment partition walls, under the fire resistance test of being burned by high-temperature flames for 2 hours, the wall did not penetrate and burn, and the gypsum board was firmly bonded to the keel. In the construction of fireproof bulkheads in shipbuilding, in the face of the combined test of high fire temperature and seawater spray, the bulkhead using this adhesive did not show the falling off of thermal insulation materials and deformation of the steel plate. In outdoor wooden landscape facilities, such as wooden boardwalks in parks, the adhesive of the embodiment was used to fix the wooden boards, and there was no loosening or gluing for three years, and it did not burn extensively under the burning of a small cigarette butt flame, successfully expanding the application of adhesives in different scenarios and meeting diverse needs.

[0085] Table 1: Comparison of experimental data of each example and comparative example

[0086]

[0087] It can be clearly seen from the above table comparison that there are differences in the key performance between each example and the ordinary preparation method in different actual application scenarios. At the level of fire safety, the flame-retardant and waterproof urea-formaldehyde resin adhesive of the present invention has achieved remarkable results. The interior decoration of buildings and the spaces in shipbuilding are densely populated or relatively enclosed, with great fire hazards and serious harms. The oxygen index of ordinary adhesives is low, and they are easy to assist combustion when encountering fire, while the oxygen index of the adhesive in the example is as high as 31-33%. Whether it is the wall decoration of hotel rooms or the bonding of thermal insulation boards in ship engine rooms, it can effectively delay combustion and prevent the penetration of flames, winning crucial time for personnel evacuation and fire-fighting operations, greatly improving fire safety protection and reducing the risk of life and property losses caused by fires.

[0088] From the perspectives of service life and application scenarios, this adhesive also has significant advantages. Ships are long-term eroded by seawater, and furniture faces daily humidity changes. The high water absorption rate of ordinary adhesives causes their performance to decline rapidly, while the water absorption rate of the adhesive in the example is as low as 6.5-7.5%, greatly extending the service life of materials and reducing maintenance costs. In terms of application, ordinary adhesives are difficult to meet the stringent requirements of special scenarios, while the adhesive of the present invention can be widely applied in scenarios such as building fire compartment partition walls, ship fireproof bulkheads, and outdoor wooden landscape facilities, relying on good flame retardancy, waterproofing, and bonding properties, meeting diverse actual needs.

[0089] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A flame retardant and waterproof urea-formaldehyde resin adhesive, characterized in that: The invention is prepared from the following raw materials in parts by weight: 100-120 parts of urea, 180-220 parts of formaldehyde-37% aqueous solution, 10-15 parts of melamine, 8-12 parts of ammonium dihydrogen phosphate, 3-5 parts of polyvinyl alcohol, an appropriate amount of sodium hydroxide, an appropriate amount of ammonium chloride, and 150-200 parts of water, wherein the urea is granular urea with an industrial purity of not less than 99% and a particle size range of 0.5-1.5 mm to ensure that it can be quickly and evenly dissolved in the reaction system, the impurity content of the formaldehyde aqueous solution is less than 0.5%, and the methanol content in the formaldehyde aqueous solution is controlled at 0.1%-0.3% to optimize the reaction process.

2. The flame retardant and waterproof urea-formaldehyde resin adhesive according to claim 1, characterized in that: The molar ratio of urea to formaldehyde is 1:1.5-1.8, and during the reaction, formaldehyde is added in batches, with the first addition amount being 80%-90% of the total amount, and the remaining part is slowly added dropwise during the polycondensation reaction stage based on intuitive phenomena such as the foam state and color change in the reaction system, combined with the viscosity change, to accurately control the reaction rate and product structure.

3. The method for preparing the flame retardant and waterproof urea-formaldehyde resin adhesive according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1, prepolymerization reaction: in a reactor equipped with a stirrer, a thermometer and a reflux condenser, add formaldehyde solution and water, stir evenly, adjust the pH value to 7.5-8.5 with sodium hydroxide solution, then add 60%-70% of the total amount of urea, heat to 80-85°C, and keep the temperature for reaction for 30-40 minutes. During this process, the stirring speed is controlled at 150-200 rpm, and the pressure in the reactor is maintained at 0.05-0.1MPa to promote efficient reaction; S2, polycondensation reaction: adjust the pH value of the reaction system to 4.8-5.2 with ammonium chloride solution, raise the temperature to 90-95°C, and carry out polycondensation reaction. When the viscosity reaches 0.1-0.15 Pa·s, add the remaining urea and continue the reaction for 15-20 minutes. During the reaction, in addition to continuously monitoring the conductivity change of the system, the transmittance change of the reaction system is also monitored online to assist in judging the reaction progress and ensure that the reaction reaches the expected level; S3, flame retardant and waterproof modification: add melamine and ammonium dihydrogen phosphate into the reactor, stir evenly, and react at 90-95℃ for 30-40 minutes. During this period, ultrasonic assisted dispersion is used with a frequency of 20-40kHz. At the same time, the power density of the ultrasonic wave is controlled at 0.5-1.5W / cm 2 , so that the flame retardant and waterproof additives can be more evenly dispersed in the system, enhancing the modification effect; S4. Post-treatment: After the reaction is completed, the temperature is lowered to 50-60°C, the pH value is adjusted to 7.0-7.5 with sodium hydroxide solution, and then polyvinyl alcohol is added. After stirring and dissolving, stirring is continued for 30-40 minutes to obtain a finished flame-retardant and waterproof urea-formaldehyde resin adhesive. The post-treatment stage is carried out under a nitrogen protective atmosphere, and the flow rate of nitrogen is controlled at 10-20L / min to prevent the adhesive from being oxidized or interfered by other impurities during the later treatment process.

4. The method for preparing a flame retardant and waterproof urea-formaldehyde resin adhesive according to claim 3, characterized in that: In the prepolymerization stage, the viscosity of the reaction system is measured by a professional rotational viscometer to control the degree of reaction. The selected rotational viscometer has an accuracy of ±0.001 Pa·s, a rotor model of No. 2, and a rotation speed of 60 rpm. Before measuring the viscosity, the viscometer needs to be calibrated to ensure the accuracy of the measurement data.

5. The method for preparing a flame retardant and waterproof urea-formaldehyde resin adhesive according to claim 3, characterized in that: During the flame retardant and waterproof modification stage, Fourier transform infrared spectroscopy is used to monitor the degree of reaction, and the change of characteristic peaks is observed to judge the degree of reaction. FT-IR spectrum data is collected every 10 minutes. When analyzing the spectrum data, not only the intensity of the characteristic peak representing the cross-linked structure of melamine and urea-formaldehyde resin is paid attention to, but also the change of peak shape, peak position shift, etc. are combined to comprehensively judge whether the reaction is basically completed.

6. The method for preparing a flame retardant and waterproof urea-formaldehyde resin adhesive according to claim 3, characterized in that: During the prepolymerization and polycondensation stages, an online infrared spectrometer is used to monitor the changes in functional groups in the reaction system in real time. By analyzing the intensity and displacement of the characteristic peaks of specific functional groups, the progress and extent of the reaction can be accurately determined, so as to more accurately control the reaction time and conditions and ensure the consistency and stability of the product.

7. The method for preparing a flame retardant and waterproof urea-formaldehyde resin adhesive according to claim 3, characterized in that: In the post-processing stage, the finished flame-retardant and waterproof urea-formaldehyde resin adhesive is filtered using a microporous filter with a pore size of 0.1-0.5 microns to remove impurities, unreacted particles, and agglomerates that may exist in the adhesive, thereby improving the purity and uniformity of the adhesive, and further improving the quality and performance of the adhesive, ensuring better bonding effect and stability in practical applications.

8. The flame retardant and waterproof urea-formaldehyde resin adhesive according to claim 1, characterized in that: The adhesive layer formed after curing has good flexibility. Through the flexibility test, its flexibility index reaches 1-2mm. It can effectively resist the internal stress caused by deformation of the substrate, prevent cracking of the adhesive layer, and improve the durability of the bonding structure.

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